Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardias which are frequently caused by the presence of an "arrhythmogenic site" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart. The heart includes a number of normal pathways which are responsible for the propagation of electrical signals from the upper to lower chambers necessary for performing normal systole and diastole function. The presence of an arrhythmogenic site or an accessory pathway can either bypass or short circuit the normal pathway, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Treatment of tachycardias may be accomplished by-a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a physician to accurately steer the catheter to the exact site for ablation. Once at the site, it is important for a physician to be able to control the emission of the energy dispersed, to ablate the tissue within the heart.
The particular interest of the present invention are radiofrequency (RF) ablation protocols, which have been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia, by neurosurgeons for the treatment of Parkinson's disease, and also by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains, while exposing a patient to minimal side effects and risks. Radiofrequency catheter ablation is generally performed after conducting an initial mapping study, where the locations of the arrhythmogenic site and/or accessory pathway are determined. After a mapping study, an ablation catheter is usually introduced to the target heart chamber and is manipulated so that the ablation tip electrode lies exactly at the target tissue site. Radiofrequency energy, or other suitable energy, is then applied through the tip electrode to the targeted cardiac tissue, in order to ablate the tissue of arrhythmogenic site or the accessory pathway. By successfully destroying that tissue, the abnormal signal patterns responsible for the tachycardia may be eliminated.
The impedance usually rises at the tissue contact site when RF energy is delivered through an electrode. To create a deeper and larger lesion, the surface of the tissue contact sites needs to maintain a proper temperature through the use of a cooled fluid irrigation or infusion to partially compensate for the temperature rise due to RF energy delivery. The following U.S. patents have disclosed the use of irrigation ports in different manners to cool the tissue contact surface. Those patents are U.S. Pat. No. 5,545,161 to Imran, U.S. Pat. No. 5,462,521 to Brucker et al., U.S. Pat. No. 5,437,662 to Nardella, U.S. Pat. No. 5,423,811 to Imran et al., U.S. Pat. No. 5,348,554 to Imran et al., and U.S. Pat. No. 5,334,193 to Nardella. In practice, the fluid coming out of the irrigation ports may not evenly cover all the surface area of the electrode or the tissue to be ablated. Furthermore, none of the above patents discloses an irrigation system of cooled fluid through a rotatable electrode means to form a uniform protective fluid layer around the electrode.
The tip section of a catheter is referred to herein as the portion of that catheter shaft containing at least one electrode. In one embodiment, a catheter utilized in the endocardial radiofrequency ablation is inserted into a major vein or artery, usually in the neck or groin area. The catheter is then guided into an appropriate chamber of the heart by an appropriate manipulation through the vein or artery. The tip of the catheter must be manipulatable by a physician from the proximal end of the catheter, so that the electrodes at the tip section can be positioned against the tissue site to be ablated. The catheter must have a great deal of flexibility in order to follow the pathway of the major blood vessels into the heart. It must permit manipulation of the tip by a user even when the catheter body is in a curved or twisted configuration.
The tip section of a conventional electrophysiology catheter that is deflectable usually contains one large electrode about 4 mm in length or longer for ablation purposes. The lesion is generally not deep, because of the potential impedance rise of the tissue in contact with the "stationary" catheter electrode and thereafter, the ablation time needs to be cut short. The word "stationary" means that the contact point of the electrode, with any tissue, remains at the same point. In some cases, the contact of a stationary electrode of the conventional catheter with tissues, reportedly results in potential tissue adhering to the said electrode. A rollable electrode is needed to reduce the tissue contact impedance rise and the temperature rise by slightly moving the rollable electrode around in a micro-moving manner so that the temperature rise is decreased by the surrounding fluid, or by the cold irrigation fluid. Even in the case of a conventional catheter having irrigation capabilities by utilizing an irrigation port, the cooled fluid does not evenly and uniformly rinse the electrode, because the electrode is not rotatable or rollable, and the constant contact point of a stationary electrode with a tissue prevents fresh cold fluid from coming into place.
Avitall in the U.S. Pat. No. 5,242,441, teaches a rotatable tip electrode. The said electrode is secured to a high torque wire for rotation and electrical conductivity. The tissue contact region is always the same unless the electrode is rotated by an external mechanism intermittently. The potential coagulum at the contact region due to impedance rise does not go away because of the relatively stationary position of the rotatable tip electrode and the absence of fluid irrigation.
Organ in the U.S. Pat. No. 5,643,255, discloses a catheter whose tip electrode is axially rotatable. In both of the above-mentioned patents, the rotation of the tip electrode is accomplished by a manual rotating action externally, which is cumbersome. There is a need for a catheter which contains at least a rollable electrode by purely moving the catheter around.
While a radiofrequency electrophysiology ablation procedure using an existing catheter has had promising results, the tip section of a known catheter usually has a fixed non-rollable electrode and a fluid infusion port which may not evenly rinse the electrode when contacting the tissue for ablation purpose. Therefore there is a need for an improved catheter and methods for making a deeper and larger lesion in the cardiac tissue.